A phased array antenna is an array of antennas in which a relative phase of signals feeding each antenna is varied such that an effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions to provide electronic steering of a beam. To convert a reflector array into a beam steerable antenna, a phase shift distribution provided by spatial phase shifting pixels is dynamically changed depending on the direction of the desired output beam in the far field.
Beams are formed by shifting the phase of the signal emitted from each radiating element to provide either constructive or destructive interference to steer the beam. These antenna systems come in different sizes and scales due to several factors such as frequency and power requirements. High-power phased array antenna technology that yields an affordable system is a major problem in the commercial and military wireless industry. The cost of current phased array antenna technology is a major factor that limits application to the most expensive military systems. Additionally, the solid-state technology that lies at the heart of current phased array antenna technology has inherent limitations when it comes to power and heat handling capability due to the generation of a large amount of heat.
One of the desirable features that reflective array antennas offer is beam collimation using planar structures or structures that can conform to the outer surface of a given platform. A typical reflective array antenna consists of an array of terminated, unidirectional radiating elements operating as scatterers. When illuminated with a suitably-designed feed antenna, each element of the array scatters the wave with a different phase shift (or time delay) and amplitude. Collectively, the amplitude and phase (or time delay) responses of the elements are designed to provide beam collimation over the reflective array antenna's aperture. This way, a reflective array antenna can be thought of as an aperture populated with a number of discrete spatial phase shifters or spatial time delay units. Various techniques have been used to design reflective array antennas based on the design of the spatial phase shifters or time delay units that they use.